Ballistic and blast resistant armor panels are well known and take on a variety of configurations for providing armor to buildings, vehicles, ships, airplanes and a variety of other applications where armor is required. In addition to typical projectiles, it is also desirous to stop high velocity armor piercing weapons.
Most armor piercing projectiles rely on a hard material in a pointed rod-like form (e.g. hardened steel, tungsten carbide). Many are fired from conventional weapons, and have a soft metal casing of copper or lead. The actual armor piercing element is considerably smaller than the caliber of the weapon. For example an M-993AP round is 30 caliber, with a diameter of 0.300″, and a hard tungsten carbide penetrator 0.221″ in diameter encased in copper. The point of the penetrator develops very high stress on contact, while the hard nature of the penetrator material allows it to maintain high stress without failing, causing the target to fail (crush, deform, melt, or vaporize). Further, the long rod-like shape allows a large amount of kinetic energy to be applied to a small area.
One method used to defeat an armor piercing threat is to use a hard surface to blunt, crack, and/or fragment the projectile so that it can then be stopped more easily. For example, a ceramic may be used as the first surface, with a metal such as aluminum as the second layer, and a composite material laminate as a layer to catch the fragments.
Attempts have been made to facilitate deflection (and rotation) of projectiles. Examples include an array of ceramic balls, in two or more non-aligned layers, to create a somewhat torturous path for the penetrator, in which it is not possible to find a straight path that intersects a ball surface at an angle. The balls need to be of substantial weight in comparison to the projectile in order to have a significant effect, and such weight is not efficient.
Another design uses short ceramic cylinders with rounded ends, suspended in a soft matrix, but suffer similar shortcomings as the array of balls. Other attempts include a wavy surface, with peaks and valleys, some with a spherical indentation in a square ceramic tile, to thicken the tile in the corners and try to offer non-flat surfaces. All of these attempts have fallen short of providing the glancing effect at all positions on a panel and at all trajectory angles. There is always a way to hit the panel at 90° to the primary stopping interface, at some position and angle.
In U.S. Pat. No. 5,007,326, metal layers with holes present oblique surfaces to the projectile in an effort to break up the projectile.